We describe the current status of the HIFI mixer units for Band 3 and Band 4. The mixer units cover the 800-960 GHz and 960-1120 GHz frequency range and have a 4-8 GHz IF frequency band. The major requirements and the design strategy are described. Functional tests of the magnet, the de-flux heater, IF-circuit, and the corrugated horn were performed. Details of the design of the mixer units and the performance status are presented. The DSB receiver noise performance ranges from 210 K at 850 GHz to 430 K at 1075 GHz.

Gert de Lange, SRON National Institute for Space Research (Netherlands)Brian D. Jackson, SRON National Institute for Space Research (Netherlands)M. Eggens, SRON National Institute for Space Research (Netherlands)H. Golstein, SRON National Institute for Space Research (Netherlands)Marinus Jochemsen, SRON National Institute for Space Research (Netherlands)W. M. Laauwen, SRON National Institute for Space Research (Netherlands)L. de Jong, SRON National Institute for Space Research (Netherlands)